The field of this invention relates to reducing power dissipation in a synchronous switching regulator. More specifically, this invention relates to systems and methods for controlling the charge profile remaining in the body diode of a synchronous switching transistor at the time of its forced commutation by the main switching transistor.
A synchronous switching regulator includes two switching transistors that are switched ON and OFF out of phase with one another by a control circuit. The switching transistors include a main switching transistor and a synchronous switching transistor. When the synchronous switching transistor is turned OFF in each cycle, the channel current of the synchronous switching transistor moves into its body diode. A short time later, the main switching transistor turns ON, and a reverse recovery current flows through both switching transistors. The reverse recovery current increases rapidly to a large value causing substantial power dissipation, because the body diode of the synchronous switching transistor has not yet commutated.
It would therefore be desirable to provide a synchronous switching regulator that reduces the rate of rise in the reverse recovery current and the maximum current in both switching transistors at the time of commutation of the body diode of the synchronous switching transistor.
It would also be desirable to provide a synchronous switching regulator that reduces power dissipation by controlling the profile of the charge remaining in the body diode of a synchronous switching transistor at the time of its forced commutation by the main switching transistor.
It would also be desirable to provide a synchronous switching regulator that reduces power dissipation in the switching transistors whether it is operated as a buck or a boost regulator.
It is an object of the present invention to provide a synchronous switching regulator that reduces the rate of rise in the reverse recovery current and the maximum current in both switching transistors at the time of commutation of the body diode of the synchronous switching transistor.
It also is an object of the present invention to provide a synchronous switching regulator that reduces power dissipation by controlling the profile of the charge system remaining in the body diode of a synchronous switching transistor at the time of its forced commutation by the main switching transistor.
It is also an object of the present invention to provide a synchronous switching regulator that reduces power dissipation in the switching transistors whether it is operated as a buck or a boost regulator.
The present invention provides systems and methods for controlling the current through body diodes of switching transistors. Switching regulators of the present invention include an inductor that is coupled in the commutation path of the body diode of the synchronous switching transistor. The inductor controls the charge profile of the body diode of the synchronous switching transistor at the time the body diode commutates to reduce power dissipation by slowing down the rate of rise in the reverse recovery current. The inductor reduces the maximum reverse recovery current through both switching transistors reducing power dissipation, especially in the main switching transistor.
Switching regulators of the present invention that may be used as buck or boost include two inductors that are coupled to each of the switching transistors. The first inductor reduces power dissipation in one switching transistor when the regulator is operated as buck regulator. The second inductor reduces power dissipation in the other switching transistor when the regulator is operated as a boost regulator. A diode and a recovery switcher may be used in the present invention so that the energy stored in the inductor may be dissipated when the body diode turns OFF.